1. Field
The present disclosure relates to a semiconductor device, in particular to a semiconductor device that is a power conversion module accommodating a plurality of switching elements connected in series in a package and connecting plural sets of the plurality of series-connected switching elements in parallel to increase current carrying capacity of the semiconductor device.
2. Description of Related Art
Semiconductor devices for power conversion often use insulated gate bipolar transistors (IGBTs), which are power switching elements exhibiting excellent operation performances in high voltage, heavy current and high speed switching. A semiconductor device having a multilevel inverter circuit is known to meet the requirements for down-sizing and high performance. The multilevel inverter circuit outputs multi-levels of voltages in combination of plurality of IGBTs, and is disclosed in Japanese Unexamined Patent Application Publication No. 2000-060140, for example.
FIG. 7 is a circuit diagram of a one phase, three-level inverter circuit of a general construction using switching elements of IGBTs. FIG. 8 is a circuit diagram of a first example of a three-level inverter circuit with increased current carrying capacity, and FIG. 9 is a circuit diagram of a second example of a three-level inverter circuit with increased current carrying capacity.
The three-level inverter circuit of FIG. 7 comprises: four IGBTs 101, 102, 103, and 104; four free-wheeling diodes 105, 106, 107, and 108; and two clamping diodes 109 and 110. The IGBTs 101, 102, 103, and 104 having respective antiparallel-connected free-wheeling diodes 105, 106, 107, and 108 are each composed of a discrete module.
The IGBTs 101, 102, 103, and 104 are connected in series and the middle node is connected to an output terminal 111. A node between the IGBT 101 and the IGBT 102 composing an upper arm of the inverter circuit is connected to a clamping diode 109. A node between the IGBT 103 and the IGBT 104 composing a lower arm of the inverter circuit is connected to a clamping diode 110. The clamping diodes 109 and 110 also compose a module.
The emitter terminal of the IGBT 104 is connected to the negative terminal potential N of a power supply. The collector terminal of the IGBT 101 is connected to the positive terminal potential P of the power supply. The node between the clamping diodes 109 and 110 is connected to the middle potential M of the power supply.
A voltage having three-levels of potential in each of the positive and negative sides is delivered from the output terminal 111 by ON/OFF-controlling the IGBTs 101, 102, 103, and 104. Each of the IGBTs 101, 102, 103, and 104 is a module having a current carrying capacity corresponding to the rated output of the inverter circuit.
When each of single IGBT 101, 102, 103, and 104 cannot supply enough current carrying capacity, a plurality of IGBTs are connected in parallel. In the example of FIG. 8, the upper arm of the inverter circuit is composed of two sets of series-connected modules, one set being composed of a module of an IGBT 101a and a module of an IGBT 101b connected in parallel, and another set being composed of a module of an IGBT 102a and a module of an IGBT 102b connected in parallel. The lower arm of the inverter circuit is composed of two sets of series-connected modules, one set being composed of a module of an IGBT 103a and a module of an IGBT 103b connected in parallel, and another set being composed of a module of an IGBT 104a and a module of an IGBT 104b connected in parallel.
In the construction of the inverter circuit, the modules are prepared separately and then assembled together, leading to complicated wiring. In addition, drive circuits have to be prepared individually.
FIG. 9 shows another example of an inverter circuit. This inverter circuit is not composed of a combination of a plurality of modules but is formed of a single module that is composed of a plurality of chips combined together. The inverter circuit of FIG. 9 is composed of two sets of circuits, each set being composed of series-connected chips and being similar to the inverter circuit of FIG. 7.
The upper arm of the inverter circuit comprises series-connected IGBT chips 121 and 122 and series-connected IGBT chips 131 and 132 that are connected in parallel to the series-connected IGBT chips 121 and 122. The lower arm of the inverter circuit comprises series-connected IGBT chips 123 and 124 and series-connected IGBT chips 133 and 134 that are connected in parallel to the series-connected IGBT chips 123 and 124. In the parallel connected circuit in the upper arm, the corresponding IGBT chips 121 and 131 have a common gate terminal 141 and a common auxiliary emitter terminal 151; and the corresponding IGBT chips 122 and 132 have a common gate terminal 142 and a common auxiliary emitter terminal 152. Likewise, in the parallel connected circuits in the lower arm, the corresponding IGBT chips 123 and 133 have a common gate terminal 143 and a common auxiliary emitter terminal 153; and the corresponding IGBT chips 124 and 134 have a common gate terminal 144 and a common auxiliary emitter terminal 154.
The auxiliary emitter terminal 151 is connected to the emitter of the IGBT chip 121 and further to the emitter of the IGBT chip 131 through an auxiliary emitter line 161. The auxiliary emitter terminal 152 is connected to the emitter of the IGBT chip 122 and further to the emitter of the IGBT chip 132 through an auxiliary emitter line 162. Likewise, the auxiliary emitter terminal 153 is connected to the emitter of the IGBT chip 123 and further to the emitter of the IGBT chip 133 through an auxiliary emitter line 163. The auxiliary emitter terminal 154 is connected to the emitter of the IGBT chip 124 and further to the emitter of the IGBT chip 134 through an auxiliary emitter line 164.
The node between the IGBT chips 122 and 123 is connected to the node between the IGBT chips 132 and 133 through an output line 171, and the node between the IGBT chips 132 and 133 is connected to an output terminal 111 through an output line 172.
The clamping diode 125 is connected to the node between the IGBT chips 121 and 122, and the clamping diode 126 is connected to the node between the IGBT chips 123 and 124. The clamping diode 135 is connected to the node between the IGBT chips 131 and 132, and the clamping dode 136 is connected to the node between the IGBT chips 133 and 134. A voltage with three-levels of potential in each of positive and negative sides is delivered from the output terminal 111 by ON/OFF-controlling the IGBT chips 121 and 131, the IGBT chips 122 and 132, the IGBT chips 123 and 133, and the IGBT chips 124 and 134.
In the construction of parallel-connection of series-connected circuits, imbalance of operation of corresponding IGBT chips generates a potential difference between both ends of the auxiliary emitter line, which may destroy the auxiliary emitter line by abnormal current. For example, the four IGBT chips 121, 122, 131, and 132 of the upper ram in FIG. 9 have not necessarily equivalent characteristics, but for example ON resistances are different in the ON operation. Suppose that the IGBT chips 121 and 132 exhibit relatively low ON resistance and the IGBT chips 122 and 131 exhibit relatively high ON resistance. Then, the IGBT chip 121 with lower ON resistance tends to carry larger current than the IGBT chip 131 with higher ON resistance; and the IGBT chip 132 with lower ON resistance tends to carry larger current than the IGBT chip 122 with higher ON resistance. As a result, the current supplied from the positive potential terminal P flows in larger amount through the path of IGBT chip 121, the auxiliary emitter line 161, and the IGBT chip 132 to the output terminal 111. The current flowing in the auxiliary emitter line 161 generates potential difference between both ends of the auxiliary emitter line. As a consequence, although the same gate voltage is applied between the gate terminal 141 and the auxiliary emitter terminal 151, the voltage between the gate and emitter of the IGBT chip 121 differs from the voltage between the gate and emitter of the IGBT chip 131. Thus, the IGBT chips 121 and 131 perform different operations. In addition, the auxiliary emitter line 161 with a small current carrying capacity may burn out with a heavy current.